When he was playing an atom aged player, he recorded 200 points in 50 games.[1] He started his hockey career with the Cole Harbour Red Wings in Bantam AAA and played 2 seasons with them. During that time, he recorded 145 points in 110 seasons respectively. He also played for Shattuck-Saint Mary's in Bantam AAA and Midget AAA for 2 seasons. He scored 101 points in 58 games played that he played to finish second in team scoring in their Bantam Tier I program.

On June 4, 2011, He was drafted first overall by the Baie-Comeau Drakkar in the 2011 QMJHL Draft.[2] On July 13, 2011, His rights were traded to the Halifax Mooseheads for Carl Gélinas, Francis Turbide, the Mooseheads' first round draft picks in 2012 and 2013, and the Quebec Remparts' first round draft pick in 2013 which was previously acquired by Halifax.[3] On May 26, 2013, He led the Mooseheads to their first Memorial Cup championship win and scored a hat-trick in the final game against the Portland Winterhawks. He was named the Most Valuable Player and scored a tournament-best seven goals and six assists in four games as well earned a spot on the Tournament All-Star Team.[4]

On June 30, 2013, he was drafted by the Colorado Avalanche with the 1st overall pick in the 2013 NHL Entry Draft.[5] On July 9, 2013, the Avalanche signed MacKinnon to his first NHL contract, a three-year entry level deal.[6]